Voltage control of a vibratory pump - Page 2

December 9th, 2009, 1:54 am

Hi guys,
I must confess, when I installed the dimmer last night, I didn't really understand how they worked. I did some research, found this page
http://www.epanorama.net/documents/ligh ... immer.html

I thought that the amplitude of the voltage was lowered, I didn't know that the dimmer is actually pulling the voltage to ground for part of the waveform.

Based on Cecil's description of a vibe pump (thanks for providing that information), I would think that the dimmer thinks the voltage has a lower amplitude, when it sees the waveform out of the dimmer.

I am a little worried, that the dimmer won't play well, long term, with the pump motor. Haven't decided if I'm going to do something about it or not.

For the zero crossing idea, I stole it from this thread
DIY PID-Controller with microcontroller
It appears to be working for him, but I don't know how it was implemented there.

I played with my pressure dimmer a little more tonight, I was able to adjust it down to 4 bar, and still get flow.

And as for the thing that started this, trying to get better temp stability during the shot, I still think I see more people that think it's a good thing.
I have not seen any blind tests, that I can remember, one way or another. I may try my gaggia, with and without the preheater, but it won't be a blind test, and I am far, far from being an expert on espresso.

Randy

#12: Post by **Billc** » December 9th, 2009, 2:44 am

Randy,
Taste is the real key. Temp stability is kind of the wrong term to apply to the temperature. It is really temperature consistency. The key is repeatability. Temperature stability (i.e. flat line) came about because this was the best way known at the time to make the machines consistent. It turns out that lever machines have fairly consistent temperature profiles during the extraction. To me a good machine has a reproducible temp profile so you can take the machine variable out of the equation.

Bill

#13: Post by **cafeIKE** » December 9th, 2009, 12:46 pm

I installed a heater cut-out relay to solve this very problem. What problem? The relay has been disabled for 3 years.
IMO, it's measureable, but not tastable.

#14: Post by **ira** » December 9th, 2009, 11:15 pm

Unless I'm wrong which is possible a vibe pump is essentially just a solenoid with a hollow piston and a couple of valves. In my playing with solenoids I've always found it takes quite a bit of voltage to get them to start moving and then you almost can't turn it off fast enough to keep them from slamming all the way in. Something like the force increases or decreases as the square of the distance. So the easiest way to modulate a vibe pump is with variable frequency. Probably being able to smoothly adjust the frequency between 30 and 60 PPM would answer the question if it's a reasonable solution. A diode or 4, a decent sized capacitor, a 555, a power transistor or two and a few more parts should get you enough to prove the idea. That's not the safest way to do it and if it works you'd want to come up with something less likely to electrocute the user.

The thing about a lamp dimmer is it delays the application of power during each 1/2 cycle and so it controls the pump by reducing how far the piston moves, but you'll likely find that it does nothing over big ranges and then get's really sensitive.

I still think the best answer might just be putting a restriction between the pump and the OPV. Piston pumps are perfectly happy running at maximum pressure and low flow. Might have the happy side effect of quieting it down because the piston will be moving less.

Ira

December 10th, 2009, 10:42 am

cafeIKE wrote:I installed a heater cut-out relay to solve this very problem. What problem? The relay has been disabled for 3 years.
IMO, it's measureable, but not tastable.

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Thanks for the info. I can pretty easily add a switch, should only take a few minutes, and then it will be easy to try it both ways. How much does you pressure vary when the heater turns on?

Ira
When I read your first post, I wasn't sure what you meant, then I saw Ken's post of fixing a problem in a gicleur, and he described what it was, so I figured out what you meant. Basically, add a restrictor, to lower the pressure/flow out of the pump. It would work, but I'm still not quite sure how I would build one.

The timer would work too, but my dimmer is working well enough, I can adjust the pressure to 9 bars, so I'm not that motivated to build a timer circuit to power the pump. The dimmer is a little sensitive, but not overly so, I don't have any problems adjusting to the pressure I want.

My next change will be to add a pressure gauge to my gaggia. I have been figuring out how to do it, I need a 2.5" hole saw, a T, and one special adaptor.

Randy

#16: Post by **cafeIKE** » December 10th, 2009, 3:37 pm

randytsuch wrote:How much does you pressure vary when the heater turns on?

I forget what the digital gauge measured, but the panel gauge barely moves, maybe 0.1 or 0.2bar. Safely say < 0.3bar.